1. Field of the Invention
The present invention relates to mounting of a lens, and more particularly concerns mounting of a refractive lens element having a very thin edge thickness in a manner that enables the lens to withstand shock loads.
2. Description of Related Art
In the design of refractive optical systems there are often required lens elements whose edge thicknesses are exceedingly thin. Conventional mounting of such a lens element involves support of the element at its perimetrical edge. Commonly a shoulder or annular lens support cell is mounted in the optical system housing, and the lens edge is positioned against the support cell with a threaded ring being screwed into the housing to axially press against the lens edge and hold the lens in place in the housing. However, such a mounting is not sufficiently robust and will not allow the lens to withstand heavy shock loads, such as those that may be experienced by an optical gun sight system mounted on a gun turret, for example. Use of a bonding material at the lens edge will provide insufficient support because of the necessarily limited radial extent and rigidity of the usual bonding material and the thin cross-section adjacent to the bond. The bonding material, of course, cannot extend any significant distance along the surface of the lens as it may place unacceptable restraint on thermally induced expansion and contraction of the lens material. If the bonding material is sufficiently strong and rigid to support expected shock loads, the lens element may very well be subject to failure because of shocks and thermal loading on its thin cross-section. Generally for precise axial positioning the bonding material is relatively rigid, and when subject to thermal stresses because of temperature changes, may exert unacceptably large stresses on the lens itself. For these reasons, in the past, telescope or imaging system designs for a system that is to be subject to large shock loads have been changed and/or abandoned when the design is found to yield lens elements whose edge thicknesses are exceedingly thin.
Accordingly, it is an object of the present invention to provide for the mounting of a refractive lens element having a very thin edge thickness in such a manner that the lens element is capable of withstanding large shock loads while retaining its position, and thus alignment.